Reduction of static interference in carrier systems



April 1, 1930. D. E. BRA'NSON REDUCTION OF STATIC INTERFERENCE INCARRIER SYSTEMS Filed Nov; 15

(Carrier) 1 in? 1/11/22 610 earner} line . INVENTOR BY BEBm/nswmATTORNEY Patented Apr. 1, 1930 UNITED STATES PATENT OFFICE DAVID E.BRANSON, OF RIVER EDGE, NEW JERSEY, ASSIGNOR TO AMERICAN TELE- PHONE ANDTELEGRAPH COMI'ANY, A CORPORATION OF NEW YORK REDUCTION OF STATICINTERFERENCE IN CARRIER SYSTEMS Application filed November 15, 1928.Serial No. 319,654.

' vacum tubes by the superposition of the interfering pulse upon thenormal carrier current of the channel reduces the current which operatesthe receiving relay so that a false spacing signal may appear during amarking impulse.

In order to overcome this difliculty it has been proposed to provide inaddition to the regular receiving channels of the carrier systern, anauxiliary bucking channel in which '25 no signals are ordinarilyreceived, due to the fact that no'carrier is transmitted correspondingto this channel. When a lightning discharge occurs the auxiliary channelpicks up one of the component frequencies of the lightning discharge,which is rectified to produce a pulse corresponding to the disturbinsignal pulse occurring in the normal channe s of the system. This pulseis transmitted through auxiliary windings to each of the receivingrelays in such a direction as to tend to hold the armature of thereceiving relay upon either its marking or spacing contact, dependingupon which contact it rested against at the time the disturbing impulseoccurred.

As the direction of the effect of the correcting impulse is determinedmerely by the character of the received signal (marking or spacing) atthe time the static disturbance occurs, and is independent of Whetherthe static impulse tends to hold the armature against its contact or toshift it, it is evident that if the static impulse occurs just at thetime the signal is changing from marking to spacing or vice versa, theimpulse from the auxiliary channel may tend to prolong the marking orspacing signal by holding the armature of the receiving relay againstthe contact upon which it then rests. In accordance with the presentinvention it is proposed to utilize auxiliary channels in such a manneras to produce effects upon any given receiving relay which are oppositein direction to those produced by the static disturbance.

In order to accomplish this result, two auxiliary channels are provided,one of which is a marking channel to which a carrier current iscontinuously transmitted from the transmitting station, and the other ofwhich is a spacing channel to which no carrier is supplied. The effectof a static impulse upon the marking channel will be similar to thatupon each receiving channel during the receipt of marking signals.Similarly, the effect of the static impulse upon the spacing channelwillbe similar to that produced upon each receiving channel during thereceipt of spacing signals. By means of a reversing relay the markingchannel may be connected to a suitable windingof any given receivingrelay when it is receiving a marking signal and thereby produce in therelay an effect Which balances out the effectof a static impulse. Whenthe relay is receiving a spacing signal, however, the reversing relaywill shift the connection to the spacing channel, thereby producing aneffect in the relay opposing that of the static disturbance. In thislatter, the effect of static disturbance is neutralized or balanced outin the relay in such a manner as to enable the relayto respond to achange from marking to spacing or vice versa without any prolongation ofthe existing signal due to the effect of the auxiliary channel.

The invention will now be more fully understood from the followindescription, when read in connection wit the accom panying drawing, thefigure of which is a circuit diagram illustrating a preferred embodimentof the invention.

Referring to the figure, the various currents of the multiplex carriersystem are received in a circuit RL which may be con- I drawing, and ofthese a description of one.

for example, channel No. 2. will sutlicc. This comprises a tunedselecting circuit T asso ciated with the circuit RL for selecting thecarrier frequency f assigned to the channel. Vacuum tube amplifiers Aand A are provided for amplifying the carrier frequencies. A rectifyingvacuum tube D is also provided for translating the carrier frequencyinto di' rect current signal impulses. The grid of the Vacuum tube D isso biased by means of a C battery that with no carrier current present.no current will flow in the plate circuit. \Vhen carrier currentisapplied to the grid. however. the rectified one-way current flows inthe plate circuit of the rectifier tube D The operating winding V of thereceiving relay RR is included in the plate circuit of the rectifier. Abiasing windil'ig Y is also provided, and by means of a suitable resistance 1' the current flowing through the biasing winding is madeequal to about onehalf the current supplied from the plate of thedetector D when the carrier is being re ceived.

In the system as illustrated it is assumed that carrier current istransmitted during the marking interval and that no carrier current istransmitted during the spacing interval. Normally when no signaling istaking place the carrier current is continuously on the circuit so thata steady direct current flows through the winding W to hold the armatureof the receiving relay RR upon its marking contact in spite of thenormal biasing current through the winding \V Each time a spacing signalis transmitted by interrupting the carrier current the rectified currentthrough the winding ceases and the armature is shifted to its spacingcontact by the pull due to the biasing winding \V The efiect of alightning or other static interference upon the system so far describedis as follows: It at the time the lightning discharge occurs a spacingsignal is being transmitted so that normally no 'arrier would bepresent. the selecting device T ot the channel will pick up one of thecom poncnt frequencies of the li; ;hting discharge which corresponds tothe frequency of the channel so that this frequency will be amplitiedand impressed upon the rectifier D to produce a short pulse of directcurrent, tending to shift the armature of the receiving relay BB fromits spacing contact to its marking contact, thereby causing a falsesignal. It the lightning discharge should occur during the transmissionof a marking signal. the effect will depend upon the magni tude of theenergy of the static discharge at the frequency corresponding to thechannel. If this energy is not so large as to overload the tubes of thesystem it merely tends to pro duce a larger rectified current in theplate circuit of the rectifier l) so thatthe ctlcct upon the winding TV;is to increase the pull tending to hold the armature upon its ma rkingcontact. It. however. the energy ot' the static discharge is very large.so as to overload the various tubes of the system. thereby producingcrowdiug' of the normal carrier currents of the channels. the carriercurrent for each channel is reduced in amplitude to make room. as itwere. for the excess energy of the lightning discharge. This reductionin the carrier frequency of the particular channel now underconsideration may result in a decreased current in the plate circuit ofthe rectitier I): so that the winding \Y i no longer able to hold thearmatur aga nst the pull of the biasing winding. This ('ZlllHt a falsespacing signal.

In order to correct for these false signals. two additional channels areassociated with the circuit llli. one of the channels being a so-calledmarking channel to which a carrier current is continuou ly transmittedfrom the transmitting station and the other of which is a so'calledspacing channel and to which no carrier current is transmitted from thedistant transmitting station. The marking channel consists of aselecting circuit T for selecting the frequency f assigned to thischannel. The cl aunel also includes amplifiers MA and MA. similar to theamplifiers already tltrt'llllttl in connection with channel Xo. 2. Themarking channel also includes a dctcctor for each receiving channel ofthe system. For example. the detector Billis associated with the markingchannel tor receiving channel No. l and the detector hill is likewiseassociated with the marking channel for receiving channel No. l. 'l hesedetectors are in all respects similar to the detector I) already dt('l'lll0d and supply to their plate circuits continuous direct currentstleii-l'lllllltll by the amplitude of the received carrier.

The spacing channel dilhu-s from the marking channel in that no carriercurrent is transrritted thereto from the distant transmitting stationand its selecting circuit T is tuned to a t'requeucy which is difl ereutfrom the frequency of the marking channel and also from the variouscarrier frequencies assigned to the signal receiving channels. Thespacing channel includes amplifiers SA and SA in all respects similar tothe correspondltltf lfltl If E ing amplifiers of the marking channel.Likewise, as in the case of the marking channel, detectors, such as SDand SD are provided for each of the signal receiving channels; Nocurrent flows in the plate circuits of the detectors associated with thespacing channel under normal conditions. If, however, a static impulseoccurs, the channel selects a frequency component thereof correspondingto the frequency of the channel and thereby causes a rectified currentpulse to flow in each of the detectors associated with the spacingchannel. 7

Each receiving relay controls polar switching relays. For example, thereceiving relay RR controls polar relays PR and PR for the purpose ofreversing the circuit connections to the auxiliary channel, in a mannerto be described later. Likewise, the receiving relay RR controls polarrelays PR and PR, in a similar manner.

The operation of the marking and spacing channels may now be understoodfrom a description of their effect upon the receiving channel No. 2.Normally, with the marking signal bein received by channel N0. 2, thearmature o? the receiving relay RR will be upon its marking contact andthe polar relay PR will have its armature upon its upper contact, sothat the plate circuit of the detector MD (which is associated with themarking channel) will be connected to the biasin winding VV Thisincreases the norma biasing current due to the resistance r, by anamount determined by the amplitude of the received carrier of themarking channel. In order, therefore, to maintain the normal relationbetween the currents flowing in the operating and biasing windings, thepolar relay PP, is arranged to coir ncct to the operating winding aresistance r: in parallel with the plate circuit of the detector D theresistance 7': being so proportioned as to draw through the winding acurrent in addition to the plate current of the detector D saidadditional current having a value equal to the plate current normallysupplied to the winding Y, from the detector hlD hen a'spacing signal isrc ceived due to the interruption of the carrier frequency f supplied tochannel X0. 2, the receiving relay RR shifts the armature to its spacingcontact. thereby causing the polar relays PR; and PR to shift theirarmaturcs to their lower contacts. The polar relay PR disconnects thebiasing winding from the detector MD of the marking channel and connectssaid winding to the detector SD 'ot' the spacing channel. As no currentnormally flows in the plate circuit of the detector SD the armature ofthe polar relay PR is arranged to disconnect the resi tance 1" from theoperating winding during the spacing condition so that in the .nels, theplate current of the absence of any static disturbance no current flowsthrough the operating winding V As has already been pointed out, theeffect of static upon the signalbf any given channel depends uponwhether the channel is at that moment receiving a marking or a spacingsignal. It a marking signal is being received in channel No. 2, forexample, the polar relays PR and PR will have their contacts upon theirupper armatures so that the marking channel will be connected to thebiasing winding Under these conditions the current drawn through thebiasing wind ing W by the plate of the detector MD of the markingchannel is just balanced by the current drawn through the operating wiuding W by the resistance I'- The current drawn through the latter windingby the plate circuit of the detector D however. is substantially twicethat drawn through the winding W by the resistance 13.

NOW if the cited; of the static impulse is such as to overload the tubesin the tran nif sion circuit and cause crowding of thc thandetcctor i);will be decreased, and if it should be, decreased to such an extent thatthe total current through the winding is less than that through thewinding the armature of the reccfrinu' relay would be shifted to its'slmtii'lg' condition, thereby causing a false signal much as themarking cha nel i r carrier current, however, thl carrier c1 will bedecreased'in volume just a the car rier current supplied to channel he.2 dur ng themarking signal. oit eqitenti v. the plate current of thedetector T\ll. (and other dete tors associated with the marking channel)will be decreased accordii'igly so that there will be a decrease in thecurrcnt flowing through the winding V which conipar able to the decrea ein the current flowing through the winding It the marking signal shouldend while the static disturbance is continuing, the interruption ot' thecarrie frequency transmitt d to the receiving channel No. Q will reducethe current through th winding V: and permit the biasing sindi to shiftthe relay armature to its spacing contact not.rith;-tanding the staticinipu e.

In case the condition or" the tifzttl ili circuit such at the staticinipul; e d overload the tu es. the e'ilect upon :12. vidual channel.such as channel be to increase the plate current of the dc tor tube Dand thereby li (2itt1r-t= the curzcnt flowing through the winding c VThe eti'c t upon the marking channel, however, is to similarly increasethe plate current ot the detector tube, such as MD so that there will bea corresponding increase in the current flowing through the winding VShould the signaling channel No. 2 change from marking to spacing whilethe static impulse continues, the interruption of the carrier suppliedfrom the distant station will reduce the current flowing through thewinding N: to permit the relay to shift its armature to its spacingcontact. The shifting of the armature from marking to spacing during thecontinuance of a static impulse, resuits in shifting the armature: ofthe polar relr vs PR and PR thus establishing the circuit in conditionto neutralize the effect of static during a spacing signal.

When any channel, such as channel No. 2, is receiving a spacing signal,the armature of the olar relay PR shifts the connection of the iasingwinding from the marking channel to the spacing channel while the polarrelay PR disconnects the resistance 1' from the operating winding In theabsence of any static effect, no current will flow through the winding(the plate current of the tube D being substantially zero duringspacing), and the current flowing through the biasing winding V will beonly that drawn by the resistance 1- If a static impulse should occurWhile the circuit is in spacing condition, the selective circuit T ofchannel No. 2 would pick up a component whose frequency corresponds tothat of the channel, so that a current would flow in the plate of thedetector D and hence, in the winding W If this current should be largerthan the current drawn by the resistance r a false marking signal wouldoccur were it not for the connection over the armature of the polarrelay PR, to the plate circuit of the detector SD of the spacingchannel. Due to this connection, however, the static component picked upby the spacing channel causes a current to flow in the plate of thedetector SD and through the biasing winding V to balance the staticcurrent flowing through the operating winding W Consequently, the falsesignal will not occur. If the static impulse should con tinue after thespacing signal received by the channel had ceased and the marking signalbegun, the current flow through the operating winding W would beincreased by an amount determined by the amplitude of the receivedcarrier, thereby causing the armature of the receiving relay to beshifted to its marking contact.

It will of course be obvious that other signaling channels, such aschannel No. 1, will function in a manner similar to that alreadydescribed n connection with channel No. 2.

It will also be obvious that the general principles herein disclosed maybe embodied in many other organizations widely different from thoseillustrated without departing from the spirit of,the invention asdefined in the following claims.

WVhat is claimed is:

1. In a carrier system, a receiving channel comprising means to selectan alternat ing Carrier current, means to detect from said carriercurrent a telegraph signal, and a receiving relay responsive to saidsignal; auxiliary channel apparatus selective of com ponents ofinterfering energy differing in frequency from the carrier waves towhich the receiving channel'is selective; and connections from saidauxiliary channel apparatus to said receiving relay and controlled bysaid re eiving relay to produce in said relay, in response tointerference, electrical effects similar to but opposing those producedon said relay by the interference effect in said receiving channel.

In a carrier system, a receiving channel comprising means to select analternating carrier current, means to detect from said carrier currenttelegraph signal impulses. and a receiving relay responsive to saidimpulses; said channel producing in said relay disturbing impulses inresponse to interfering energy superposed on the system; auxiliarychannel apparatus selective of components of said interfering energydiffering in frequency from the carrier waves to which said receivingchannel is selective; and connect ons from said auxiliary channelapparatus to said receiving relay and controlled by said receiving relayto produce in said relay. in response to interference, impulses toneutraliZe the disturbing impulses from said receiving channel: saidneutralizing impulses permitting said relay to respond to changes of thedetected signal impulses.

3. In a carrier system, a receiving channel 'comprising means to selectan alternating carrier current, means to detect therefrom signalingimpulses, and a receiving relay having an operating winding responsiveto said impulses to shift the armature in one direction and a biasingwinding to shift the armature in the opposite direction: an auxiliarychannel comprising means selective of interfering components differinginfrequency from the receiving channel; a detecting means associated withsaid auxiliary channel: means to establish connections from saiddetecting means to one of said relay windings during the receipt ofmarking signals: and means to open said connections during the receiptof spacing signals.

4. In a carrier system, a receiving channel comprising means to selectan alternating carrier current. means to detect therefrom signalingimpulses. and a receiving relay having an operating winding responsiveto said impulses to shift the armature in one direction and a biasingwind ng to shift the armature in the opposite direction; an auxiliarychannel comprising means selective of interfering components differingin frequency from the receivnig channel: a detecting means associatedwith said auxiliary channel: means to establish connections from saiddetecting means to said biasing winding during the receipt of spacingsignals; and

means to open said connections during the receipt of marking signals.

5. In a carrier system, a transmission circuit, a receiving channelassociated therewith and comprising means to select an al ternatingcarrier current from said transmission circuit, mcans. to detectsignaling impulses from said carrier current, and a receiving relay; anauxiliary marking channel to which a carrier frequency different fromthat of said receiving channel is continuously supplied over saidtransmission circuit; an auxiliary spacing channel for which no carrieris supplied; said spacing channel being selective of interferingcomponents of frequency different from those of the other channels; tosaid receiving relay from said marking channel during the receipt ofmarking signals in said receiving channel, and from said spacing channelduring the receipt of spacing signals in said receiving channel.

6. In a carrier system, a transmission circuit; a receiving channelassociated therewith and comprising means to select an alternatingcarrier current from said transmission circuit; means to detectsignaling impulses from said carrier current, and a receiving relayhaving an operating winding responsive to said impulses to shift thearmature in one direction and a biasing winding to shift the armature inthe opposite direction; an auxiliary marking channel to which a carrierfrequency different from that of the receiving channel is continuouslytransmitted over said transmission circuit; said markin channelincluding means to select said frequency; a detector associated withsaid marking channel an auxiliary spacing channel for which no carrieris supplied and having selecting means to select interference componentsdiffering in frequency from the carrier frequency of said receivingchannel; a detector associated with said spacing channel; and means toestablish connections to one of said relay' windings from the detectorassociated with one auxiliary channel during the receipt of markingsignals, and from the detector associated with the other auxiliarychannel during the receipt of spacing signals.

7. In a carrier system, a transmission circuit; a receiving channelassociated therewith and comprising means to select an alternatingcarrier current from said transmission circuit, means to detectsignaling impulses from said carrier current, and a receiving relayhaving an operating winding responsive to said impulses to shift thearmature in one direction and a biasing winding to shift the armature inthe opposite direction; an auxiliary marking channel to which a carrierfrequency different from that of the receiving channel is continuouslytransmitted over said transmission circuit; said and means to establishconnections,

marking channel including means to select said fre uency; a detectorassociated with said mar in'g channel; an auxiliary spacing channel forwhich no carrier is supplied and having selecting means to selectinterference components differing in frequency from the carrierfrequency of said receiving channel; a detector associated with saidspacing channel; and means to establish con; .ections to said biasingWinding from the detector associated with said marking channel duringthe receipt of marking signals, and from the detector associated withsaid spacing channel during the receipt of spacing signals.

In testimony whereof, I have signed my name to this specification this14th day of November, 1928.

DAVID E. BRANSON.

